An element's group number tells you how many the element has.

An element's group number tells you how many valence electrons the element has.

Explanation:

In the periodic table, each element is placed in a specific location because of its atomic structure.

The elements are arranged in rows,  called a period. All of the elements in a period have the same number of atomic orbitals.

The elements are also arranged in vertical columns. Each column is called a group. The elements in each group have the same number of electrons in the outer orbital. These electrons are called as valence electrons.  Example: Group 1 elements have 1 valence electron each.

the ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (uvr) from the sun, protecting life on earth from its potentially harmful effects. when the sky is clear, there is an inverse relationship between stratospheric ozone and solar uvr measured at the earth's surface.